Tim is a stalker, or is one of the scientists in the Manhattan Project, who is implied in in-game text to have left his wife for this conquest.
The Princess is the stalker's victim, or an atomic bomb.
Awesome Music: The utterly beautiful and haunting "Maenam" theme that plays in the overworld.
Genius Bonus: Those flags are nautical flags. They have messages that are pretty interesting when directed at Tim and especially at the idea that the goal is developing the atomic bomb.
World 2: N (No)
World 3: U (You are (standing into/approaching) danger)
World 4: L (Stop instantly)
World 5: X (Stop carrying out your intentions and wait for my signal)
World 6: K (I have something important to communicate)
Some parts of the Epilogue contain references that the average consumer might miss. The quote "Now we are all sons of bitches" is probably the more recognizable, being a famous quote attached to the creation of the first atomic bomb. A little more esoteric is the concept of a magnetic monopole that is mentioned in one of the alternate texts. A magnetic monopole would be a magnet with only a north or south pole - an impossibility. Which, of course, is the point. Scientists have been chasing scientific impossibilities for centuries, trying to prove that they are real. Perpetual motion machines, magnetic monopoles, and cold fusion come to mind. The mother is waiting for the child to grow up and move past these ideas. Interesting, fission was believed to be impossible by most scientists including Einstein. The reason being is that protons are easily repelled by the nucleus of an atom thus they can't be used for chain reactions. It was a colleague that convince him that neutrons could be used instead at which point the two of them wrote FDR and told him how scientists should go about making the bomb.
It's Short, So It Sucks!: The game caught some flak for its short length, as it can be beaten in one sitting if you know the solution to all the puzzles. The one feature that adds extra gaming time is a case of Fake Longevity, as one of the secret stars requires the player to just wait for an hour, jump onto a slow-moving cloud, then wait another hour.
It Was His Sled: Towards the end of the game, the princess explodes, because she is a metaphor for the invention of the atomic bomb.
Memetic Mutation: This trope page is a metaphor for the atomic bomb!Explanation A joke (usually at the expense of Braid) about the game's handlings of symbolism, which culminate in a moment at the end of the game where the Princess is implied to be a metaphor for the atomic bombs dropped on Japan... Represented by her very suddenly exploding. In the wake of much better handled symbolism in gaming circles, detractors of this game have usually used this to point out how tacky Braid's implementation of it is, especially in retrospect.)
Once Original, Now Common: Braid's heavy emphasis on symbolism and statements on life is what helped it stand out and receive a lot of praise. Today though, with so many other games who both handle their heavy themes and allegories much more effectively, as well as games that simply make better use of symbolism becoming more and more plentiful, Braid's attempts at these now come across as clumsy, tacked on, and even unintentionally humorous.
Both of the pieces in Fickle Companion, as well as the rightmost piece in "Crossing The Gap", due to them requiring you to use tactics and gimmicks you've never seen or used before.
The second half of World 6. Most of the puzzles, while logical, are extremely complex and require a great deal of out-of-the-box thinking.
That One Sidequest: Collecting the eight secret stars can be frustrating if you don't use a guide. One of them requires the player to wait for two hours while a cloud slowly transports Tim to a secret area.
